1. Field of the Invention
This invention relates generally to filters for filtering debris, hydrocarbons, and other contaminants from water flowing into storm drains.
2. Prior Art
Storm drains are provided in streets, parking lots, gas stations, and highways for draining water runoff. Some storm drains are provided with internal filters for preventing debris, hydrocarbons, and other contaminants from entering waterways.
U.S. Pat. No. 5,720,574 to Barella shows a filter positioned inside a storm drain. The filter includes a peripheral trough surrounding a central overflow opening. A set of cartridges containing filter media are positioned in the trough. Water flowing into the drain are distributed around the trough, and pass through the cartridges before exiting through a screen on the bottom of the trough. When water flow is high, excess water overflows through the central opening without passing through the cartridges. However, gravel, leaves, and other debris accumulate on top of the cartridges and block water flow, so that a worker must reach in and dig them out by hand, which is slow and time consuming. It is also cumbersome to open the cartridges and inspect or replace the filter media. U.S. Pat. No. 5,632,889 to Tharp shows a similar filter. U.S. Pat. No. 5,480,254 to Autry et al. shows a storm drain filter that comprises a box with porous vertical walls and an opening on the bottom. It is simply placed over a storm drain, so that storm water is filtered by flowing through the vertical walls of the filter. It is made for temporary use while road surface is being constructed.
U.S. Pat. No. 5,397,464 to Hannon shows a strainer box comprising a perforated basket removably received in a housing. It has no provision for using filter media, so that it cannot filter hydrocarbons and other contaminants. It includes an inlet on one vertical side and an outlet on an opposite vertical side, so that it cannot be used in a storm drain. U.S. Pat. No. 5,069,781 to Wilkes shows a drain with a removable perforated strainer received therein. It also has no provision for using filter media. U.S. Pat. No. 4,717,475 to Brandt et al. shows a filtering device with a pair of filter cartridges received in a housing. Debris collected on top of the cartridges must be removed by hand. A filter sold as the "FOSSIL FILTER" by KriStar Enterprises comprises an annular trough surrounding a central overflow opening. Filter media is positioned between spaced apart top and bottom screens. The top screen is not securely held in place, so that it may be dislodged under strong water flow. Again, debris collected on the top screen must be dug out by hand. The filter is also difficult to open for inspecting or replacing filter media. Other filters are provided with loose filtering media, which can be washed over the central overflow opening and down the drain when the water flow is high and turbulent enough, or when the drain is backed up.